"I have to tell you that over the course of several years as I have talked to friends and family and neighbors when I think about members of my own staff who are in incredibly committed monogamous relationships, same-sex relationships, who are raising kids together, when I think about those soldiers or airmen or marines or sailors who are out there fighting on my behalf and yet feel constrained, even now that Don't Ask Don't Tell is gone, because they are not able to commit themselves in a marriage, at a certain point I’ve just concluded that for me personally it is important for me to go ahead and affirm that I think same sex couples should be able to get married."

Obama said his daughters Malia and Sasha helped him along in his "evolution."

“It’s interesting, some of this is also generational,” the president continued. “You know when I go to college campuses, sometimes I talk to college Republicans who think that I have terrible policies on the economy, on foreign policy, but are very clear that when it comes to same sex equality or, you know, believe in equality. They are much more comfortable with it. You know, Malia and Sasha, they have friends whose parents are same-sex couples. There have been times where Michelle and I have been sitting around the dinner table and we’re talking about their friends and their parents and Malia and Sasha, it wouldn’t dawn on them that somehow their friends’ parents would be treated differently. It doesn’t make sense to them and frankly, that’s the kind of thing that prompts a change in perspective.”

And here's Obama talking about how discussions with his wife, First Lady Michelle Obama, contributed to his shift in support.

“This is something that, you know, we’ve talked about over the years and she, you know, she feels the same way, she feels the same way that I do. And that is that, in the end the values that I care most deeply about and she cares most deeply about is how we treat other people and, you know, I, you know, we are both practicing Christians and obviously this position may be considered to put us at odds with the views of others but, you know, when we think about our faith, the thing at root that we think about is, not only Christ sacrificing himself on our behalf, but it’s also the Golden Rule, you know, treat others the way you would want to be treated. And I think that’s what we try to impart to our kids and that’s what motivates me as president and I figure the most consistent I can be in being true to those precepts, the better I’ll be as a as a dad and a husband and hopefully the better I’ll be as president.”

ABC just held a special at 3 p.m. to announce the major shift in policy. More excerpts will air tonight during “ABC World News with Diane Sawyer” at 6:30 p.m. and Nightline at 11:35. The full interview will air tomorrow morning on Good Morning America.

Depending on how you look at it, it's either Obama completing his personal "evolution" on the issue of gay marriage and transforming it into policy, or it's Obama flipping on the issue.

"The President is the leader of our country," Evan Wolfson, the founder and president of Freedom to Marry, told Business Insider today.

"We expect presidents to speak out on moments of moral leadership, particularly when the real lives of families are affected by discrimination that needs to change. Having this president speak out forthrightly today for the freedom to marry and explaining how his heart opened and mind changed like so many others will help move the country to fairness."

Said John Lewis, the legal director for Marriage Equality USA: "I think this vote makes crystal clear that the President of the United States needs to stand up for the freedom to marry for all American citizens."